Recovery of rare gases from synthetic ammonia plant purge gases



R. A. KOBLE 2,993,342

RECOVERY OF RARE GASES FROM SYNTHETIC AMMONIA PLANT PURGE GASES July 25,1961 2 Sheets-Sheet 1 Filed March 29, 1957 m ovm HOLVNOILOVHJ wZON mZONZOEIWDmZOU INVENTOR.

R. A. KOBLE A T TORNEVS P CO mam-TF2 2,993,342 RECQVERY F GASES FROMSYNTHETIC Ah IMDNIA PLANT PURGE GASES Robert A. Koble, Bartlesviile,0kla., assignor to Phillips Petroleum Company, a corporation of DelawareFiled Mar. 29., 1957, Ser. No. 649,508 6 Claims. (Cl. 62-22) Thisinvention relates to the separation of rare gases from gaseous mixturescontaining them. In one aspect it relates to a method for recoveringhelium and argon separately from synthetic ammonia plant purge gases.

As is well known, the rare gas argon is present in the atmosphere to theextent of about one percent and many processes for separatingatmospheric oxygen and nitrogen involve separation of argon,particularly in case the oxygen and nitrogen are to be produced as puregases. It is also known that a trace of helium also occurs in air butits separation is usually not warranted.

Synthetic ammonia manufacture involves use of air and the unreactedsynthesis gas or purge gas or gases, as they are frequently called, fromsuch a plant contains the argon from the air used. The unreactedsynthesis gas is recycled in the operation and the content of argonaccordingly increases. Since argon is an inert gas, a small fraction ofthe unreacted synthesis gas must be withdrawn as a purge gas from theoperation in order to hold down the concentration of argon. In ordinaryammonia synthesis the presence of helium presents no problem because ofits very low concentration in the atmosphere and it is usually notpresent in the natural gas used in greater than trace concentrations.

However, when manufacturing synthetic ammonia from Texas Panhandlenatural gas, the inert gas problem in ammonia purge gas is different. Asis well known, the Texas Panhandle natural gas contains an appreciableconcentration of helium and this gas, along with argon from theatmosphere, accumulates in the ammonia plant purge gases.

Because of the presence of relatively high concentrations of helium andargon in the purge gases, both. gases being inert, appreciableproportions of the purge gases must be withdrawn from the ammoniaproduction system. Because of their general utility, I have devised aprocess for recovering helium and argon separately from Texas Panhandlesynthetic ammonia plant purge gases.

An object of my invention is to provide a process for separating heliumand argon as separate products from synthetic ammonia plant purge gases.

Another object of my invention is to provide a method for the recoveryof such gases in relatively pure form.

Still another object of my invention is to provide a process for theseparation and recovery of these inert gases with the simultaneousrecovery of nitrogen, the latter being usable as recycle gas in theammonia synthesis operation.

Yet another object of my invention is to provide a method for theabove-mentioned separation of gases in which an appreciable proportionof the hydrogen content of the purge gases is also recovered for reusein the synthesis operation.

Still other objects and advantages of my invention will Patent berealized upon reading the following description which, taken with theattached drawing, forms a part of this specification.

In the drawing- FIGURE 1 illustrates, in diagrammatic form, anarrangement of apparatus parts for carrying out the process of myinvention.

FIGURE 2 illustrates, also in diagrammatic form, an arrangement ofapparatus parts for carrying out a modified version of the process ofFIGURE 1.

My invention is directed particularly to a method for recovering heliumfrom a feed gas comprising helium, argon, nitrogen and hydrogen,comprising the steps of cooling said gas to a subatmospheric temperatureat a superatmospheric pressure thereby producing liquid, separating theuncondensed gas from said liquid, the gas phase comprising helium andhydrogen passing this gas phase into an oxidation zone and thereincombining hydrogen of said gas with oxygen to form water, removing thewater from the combustion zone efiluent and recovering the resultinghelium therefrom as a product of the operation. The oxygen used in theabove-mentioned oxidation step is atmospheric oxygen or, if desired, theoxygen is the oxygen of a metallic oxide reducibie by hydrogen. Oneembodiment of the invention involves separation and recovery of argon aswell as helium.

Referring now to the drawing and specifically to FIG- URE 1, andillustrative of the operation of my process, an ammonia synthesis plantoii-gas or purge gas, from a source not shown, is passed at a pressureof about 4700 p.s.i.a. (pounds per square inch absolute) at about Fthrough a pipe 101 to an expander 102. On passing through expander 102the pressure of the gas is reduced to about 610 p.s.i.a. with thesimultaneous reduction of temperature to about -80 F. by expansion.Expander 102 can be any suitable type of expansion apparatus which isadapted for operation at such low temperatures. The expander or, as itmay be called, the expansion engine 102 can be of such type as a turbineor reciprocating expander, of which the Kapitza turbine is an example ofthe former. Suitable forms of Kapitza turbines are disclosed in US.Patent No. 2,280,585, granted April 21, 1942.

From the expander 102 the cooled gas is passed through a pipe 103 into amore or less conventional heat exchanger 104 or it is, in some cases, asmall vessel containing a heat exchange coil. In any event a sump isprovided into which any condensate produced in the expander can run sothat it can be withdrawn through a pipe 10311 for such disposal asdesired. In exchanger 104 the temperature of the gas is reduced to about'l90 F. by indirect heat exchange with a gaseous material assubsequently produced. Effluent from heat exchanger 104- at thelastmentioned temperature passes through a pipe 105 into a separatorvessel 106. Vessel 106 is provided with a heat exchange coil 109 inwhich is circulated refrigerant liquid nitrogen. This liquid nitrogenboils at a temperature of about -320 F. under atmospheric pressure, andat this temperature the refrigerant cools the contents in separator 106to a temperature of about 3l0 F. At this latter temperature a gas phaseis removed from separator .106 by way of the pipe 107 and is passedthrough heat exchanger 104 as the aforementioned refrigerant assubsequently refrigeration.

produced. The refrigerant gas from the coil in exchanger 104 issues at atemperature of about 90 F. under a pressure of about 600 p.s.i.a. Thisgas passes from a pipe 108 through an expansion valve 149 and thencethrough a refrigerant economizer 141 for the recovery of useful The gasissues from economizer 1 11 at a temperature of about 50 F. under apressure of approximately 50 p.s.i.a. and passes on under theseconditions via pipe 142 into a scrubber vessel 143.

In separator vessel 1% separation is accomplished between helium andargon, most of the hydrogen going with the helium as gas through pipe107 and some hydroge along with the major portion of the nitrogen, goingwith the argon as liquid bottoms passing through a pipe 110 into afractionator 120, to be described hereinbelow.

Air, taken into the system through a pipe 111, is compressed bycompressor 112 to a pressure of about 430 p.s.i.a. and has a temperatureof about 400 F. Compressor 112 is preferably powered by the poweravailable from the expansion engine 162. Compressed air under theabove-mentioned conditionsis passed from compressor 112 through a pipe113 to a cooler 114. In this cooler the air is cooled to about 100 F.Water condensing from the compressed air is separated in a separator 115and is Withdrawn through a pipe 115a. The air from separator 115 ispassed through a dryer 116. This dryer is provided with a soliddesiccant material such as silica gel, or the like, or if desired, aliquid desiccant such as one or more of the ethylene glycols or the likeis used. From dryer 116 dehydrated air is passed through a pipe 117 to aheat exchanger 118 in which the temperature of the air is reduced toabout l F. The temperature of the air is further decreased in a reboilercoil 119 in fractionator 120 to about l7 F. and is then passed through apipe 121 into a refrigerated heat exchanger 123. In the refrigeratedexchanger the air is chilled to a temperature of about 240 F. and it isthen passed through a pipe 122 into fractionator 120. The reboiler coil119 is an indirect heat exchanger for reboiling the contents of thefractionator with air being cooled. It is intended in this fractionatorto produce a bottoms product consisting largely of a liquid solution ofoxygen and argon. Since hydrogen, of course, boils at a temperatureconsiderably below the boiling points of oxygen and argon, the overheadgases from fractionator 120 contain nearly all of the hydrogen carriedinto the fractionator through the condensate from the separator 106.This condensate from separator 106 also contains most of the nitrogencontained in the original feed gas to the operation. Of course, a largeproportion of nitrogen is introduced into fractionator 120 as acomponent of the chilled air from pipe 122. Fractionator 122 thenseparates as an overhead product the hydrogen and substantially all ofthe nitrogen. This overhead gas issues from fractionator 1211 at atemperature of about 236 F. and pressure of about 400 p.s.i.a. Thisoverhead product stream from pipe 127 is divided into two portions, oneportion passing through a pipe 130 and the other portion through a pipe129. The portion passing through pipe 130 passes through an expander 128which is similar to the expander described above. Gas issuing fromexpander 128 possesses a temperature of about -360 F. at about 50p.s.i.a. portion of the overhead gas passes through an exchanger 131 andchills for condensation purposes the portion of overhead gas from pipe129. This chilled portion of gas is further chilled in a liquid nitrogenchilled exchanger 179 to a temperature of about -290 F. This chilledmaterial passes from exchanger 179 through a pipe 135 into a refluxaccumulator 136 from which liquid, which is largely liquid nitrogen, ispassed through a pipe 137 into the upper portion of fractionator 120 forrefluxing purposes. In case make-up nitrogen for refluxing purposes isneeded in this fractionation operation it is introduced through a pipe138. i

This very cold The expanded portion of the overhead material fromfractionator is passed from exchanger 131 through a pipe 132 into therefrigeratedexchanger 123 for chilling the compressed air prior to itsintroduction into the fractionator. The eflluent refrigerant fromexchanger 123 at a temperature of about -27 F. is passed through a pipe133 to a heat exchanger 169. The gas issues from this exchanger at about3( F. and is withdrawn from the system through a pipe 134 as a nitrogenand hydrogen containing product. This gas can be passed from pipe 134 toany desired refrigeration recovery operation after which it can be, ifdesired, recycled to the ammonia synthesis operation.

The bottoms from fractionator 120 are largely argon and oxygen butcontain a small proportion of methane and ammonia. This bottoms materialleaves fractionator 120 through a pipe 124 at a temperature of about 200F. at the fractionator pressure of about 400 p.s.i.a. These bottoms arepassed through a pressure reducing valve 186, thence through the heatexchanger 118 from which the bottoms issues at a temperature of about 50F. Pressure is further reduced in valve after which furtherrefrigeration is recovered in a refrigeration economizer 126. From theeconomizer 126 the bottoms pass on through a pipe 124 and are added tothe warm overhead gases from separator 106 in pipe 142. This combinedstream, which then contains helium, argon, oxygen, hydrogen and only avery small proportion of nitrogen and hydrocarbon, is passed into ascrubber vessel 143 mentioned above. In this scrubber water removes thefinal traces of ammonia, the aqueous ammonia being withdrawn through apipe 143a. The ammonia-free gas then leaves scrubber 143 and is passedthrough a pipe 144 at a temperature of about 100 F. under 50 p.s.i.a.into the combustion zone 146 of a waste heat boiler 145. In thiscombustion zone the hydrogen burns to water and also any methane presentburns to carbon dioxide and water. Efliuent gases from this boiler arecooled in a water cooled heat exchanger 149 and the cooled gases'pass onthrough a pipe 148 into a water knockout drum 150. Water is withdrawntherefrom through a pipe 158 and the gases are passed through pipe 151and are heated in a heat exchanger 152, and are further heated in a coil147 in boiler 145. These gases thus heated to about 500 F. are passedthrough a pipe 153 into a vessel 154 containing a catalyst 155.

In case the heated gases from pipe 153 contain an excess of oxygen, thecatalyst in this zone is such a catalyst as Baker deoxo-catalyst or, incase the gas contains an excess of hydrogen, the catalyst is, forexample, a Houdry oxi-catalyst, a metallic oxide reducible by hydrogen,such as copper oxide, or iron oxide. In any event whether the heated gasentering vessel 154 contains an excess of oxygen or an excess ofhydrogen, either one of the gases is removed and the oxygen-free andhydrogen-free gas leaves this catalyst zone through a pipe 156 andpasses through the heat exchanger 152. The cooled gas from heatexchanger 152 has a temperature of about 120 F. and is freed of carbondioxide in a caustic scrubber 157 from which the gas is passed throughpipe 159 into a dryer vessel 160. This vessel 160 is provided with asolid dessicant 161 or with a liquid desiccant, as mentioned hereinaboverelative to dryer vessel 160. Dehydrated gas from dryer 160 is passedthrough a pipe 162 at a temperature of about 100 F., is compressed in acompressor 163 and is chilled by refrigerant liquid nitrogen in arefrigerated exchanger 164 to a temperature of about 300 F. Compressor163 is intended to compress the dehydrated gas to a pressure of about2700 p.s.i.a. Thus, the chilled gas at 300 F. and 2700 p.s.i.a. entersseparator vessel 166, in which an overhead gas product is separated, andleaves the system through a pipe 167 as the helium product of theoperation, for such disposal as desired. Under some conditions, ifdesired, the helium passing through pipe 167 is passed through acharcoal adsorber, similar to adsorber 51 in FIGURE 2 thereby producinga pure product. The condensate produced in exchanger 164 G 120 in pipe134. Also, the air requirement for burning the hydrogen from the heliumin the combustion zone 14 6 is considerably reduced.

Furthermore, if desired, the separation in separator is withdrawn fromthe separator through a pipe 168 and 106 can be made at full linepressure, that is 4700 is heat exchanged with the above-mentionednitrogen and p.s.i.a. In this case refrigeration of the charge gas tohydrogen product stream in heat exchanger 169 to a the system passingthrough pipes 101 and 191 for protemperature of about 200 F. At thislatter temperaducing feed to the separator at 190 F. must be supture thebottoms product passes into a separator 170 plied from another source,as exchangers 192 and .193. from which gases are removed through anoverhead pipe 10 However, in this case the separated helium containing171 for recycling to compressor 163 while liquid is passed overhead gasand the liquid argonbottoms from septhrough a pipe 172 through anexpansion valve 173 for arator 106 can be expanded separately with theproducpassage into a fractionator 176 by way of a pipe 175. tion of thework. These separate expansions are then On passage through theexpansion valve 173 the pressure carried out in expansion engines, 194in pipe 195, and is reduced to about 500 p.s.i.a. and this pressure issuf- 196 in pipe 197, similar to that described above relative ficientin fractionator 176 to effect an excellent separato expander 102 and theavailable work so produced is tion of the argon, with the argon beingwithdrawn as a used to compress the air in compressors 199 and 200,sidestream through apipe 177. This argon product conrespectively, inconduit 19 8. In this manner only a tains only a trace of nitrogen,other gases in the system minimum amount of air is required for burningthe small having been entirely removed from the argon. Column 20 portionof hydrogen accompanying the helium while a bottoms is removed through apipe 178 for such dismajor portion of the hydrogen is recovered fromfracposal as desired. This bottoms contains only a very tionator 120through pipe 134, along with the nitrogen small proportion of the argontreated in the system as for recycling to the synthetic ammonia plant.an impure product containing materials higher boiling Another variationof the process as herein described is than argon. Overhead gases fromfractionator 176, which that in case only one pure product stream isdesired, contain some argon and nitrogen, are passed through a that is,either apure helium stream or apure argon stream, pipe 187 into thelower portion of fractionator 120 as but not both, the catalystcontaining vessel 154 is omitted. recycle material. In this case anexcess of oxygen in the gas will accom Uncondensed gases from the refluxaccumulator 136 pany the argon, leaving a pure helium product, while anare passed therefrom by way of a pipe 139 and added excess of hydrogenwill accompany the helium, thus to the material in pipe 105 prior to itsintroduction into leaving the argon as a pure product. separator 106.Another variation of my invention involves burning If desired, the mainbottoms product from fractionator the hydrogen following the expansionstep in expander 120. which is rich in atmospheric oxygen, can be re-102. In this manner the combustion zone and boiler moved from thefractionator as a side-stream through a combination 14-5, with allapparatus parts to and inpipe 188. This withdrawn material from pipe 188can, eluding dryer 1 60, would be inserted following expander ifdesired, be passed through pipe 124 and though the 102 and, of course,the substituted parts would not be expansion valve 186 and thence on topipe 142. When employed as illustrated in FIGURE 1. However, such themain oxygen containing product is withdrawn through a procedure is notdesired because all of the hydrogen is pipe 188 as a sidest-rearn, asmall bleed stream is taken removed as water without recovery of anyhydrogen from the kettle section of this fractionator through a pipewhatever for [reuse in the synthetic ammonia plant. 181 containing avalve 182 and is passed on through a Thus, in pipe 134 only nitrogenwould be recovered from valve 185 and is recycled into the ammoniasynthesis the system. gas charge stock to the system, passing throughpipe The following tabulation gives product stream compo- 103. However,in case it is desired to dispose of this sitions at various portions ofthe flow diagram illustrated small volume of bleed material from thebottom of in FIGURE 1:

EXAMPLE I Material balance, mols per hour, principal components Hydrogen5s 40.0 10.6 1.6 9.0 40.0 Helium 5 4.9 0.4 0.3 0.1 4.9 Nitrogenis 83.20.8 17.8 0.0 101.2 1.0 0.2 1.0 Argon 4 1.0 0.1 3.9 0.05 0.05 4.9 5.0OH1+NH5 1s 3 3.0 12.0 Oxygen 23.0 .1 0.1 23.0 23.0

Total 100 107.2 51.8 35 7 2 5 110. 45 1. 05 31.1 81.9

1 CH4 only in stream 144.

fractionator 120, valve 185 is closed and valve 184 in pipe 183 isopened and this bottoms bleed material is combined with the wastematerial passing through pipe 103a for such disposal as desired.

The separation carried out in separator 106 is, under some conditions,carried out at a higher pressure than 600 p.s.i.a., for example, at from1,000 to 2,000 p.s'.i.a. Under such higher pressures a portion of thehydrogen which leaves separator 106 at lower pressures with the heliumwill be forced into solution in the liquid argon and removed from thisseparator through pipe 110. In this manner a larger portion of thehydrogen is recovered In the embodiment illustrated in FIGURE 2,atmospheric oxygen is not used for burning the hydrogen to water. Toremove the hydrogen I employ a metallic oxide reducible by hydrogen forremoval of hydrogen from the helium. In FIGURE 2 a feed stock similar tothat disclosed in the above tabulation enters the systern, from a sourcenot shown, throught a pipe 11. This feed material enters the system at atemperature of about 90 F. under a pressure of 4700 p.s.i.-a. and iscooled in a heat exchanger 12 and is further cooled by expansion in anexpander 13 to about =80 F. The feed then passes by way of a pipe 14through a reboiler coil 14a from the system in the overhead gas from thefractionator in which it is further cooled to a temperature of aboutasoaasa -90 F. At -90 F. the feed passes through a'pipe 15 to a heatexchanger 16 in which condensate is separated and removed through a pipe17, the gas passing on to a refrigerated exchanger 18. In this exchangerthe gas is chilled by indirect heat exchange with refrigerant liquidnitrogen, the gas issuing "from this exchanger at a temperature of about-310 F. and it is passed through a pipe 19 into a separator 2%.Separation is carried out in this vessel at 3l0 F. under 600 p.s.i.-a.with the separated gas passing through a pipe 21 to the abovementionedheat exchanger 16. This cold gas thus assists in refrigerating the feedgas. From this exchanger the separated gas at about l F. is passedthrough a pipe 22 to an exchanger 23 in which the gas is warmedsomewhat. From exchanger 23 further refrigeration is recovered in arefrigeration econornizer 24 with the gas passing on into an ammoniascrubber 25. Water for scrubbing ammonia from the gas enters thescrubber through a pipe 26 and the aqueous ammonia solution is removedthrough a pipe 39- for such disposal as desired. The scrubber gas passesthrough a pipe 27 and is heated in an exchanger 28 to about 400 F. Thisso-heated gas passes on through a pipe 30 and is further heated in aheater 31 to a temperature of about 575 F., at which temperature the gasenters a metallic oxide containing vessel 32. By-pass pipe 29 by-passesa portion of the gas from line 27 around heater 3-1 in case temperatureadjustment of the heated gas is required. Thus, temperature of the gasentering the oxide containing vessel 32 is easily regulated.

In vessels 32 and 35 are placed quantities of metaliic oxide which arereducible by hydrogen, such as copper oxide, or such an iron oxide as FeO In these vessels the hydrogen is removed from the gas stream bycombination with the oxygen from the oxide thereby reducing the oxide tometal and with the production of water. The moist, hot gas streamissuing, for example, from vessel 32 is passed through a pipe 38 intothe aforementioned heat exchanger 28 in indirect heat exchange with thefeed gases to the oxide tower. On passing through exchanger 28 these hotgases are cooled from about 575 F. to about 440 F. and are then passedinto a caustic washer vessel 40 in which aqueous caustic, from a pipe41, washes the gases with the result that the gases are cooledto about100 F. Used caustic solution is Withdrawn through pipe 72. Pressure incaustic washer 40 is about 390 p.s.i.a. and at this pressure the gasespass on through a pipe 42 and are dried in a dryer 43. This dryer ischarged with a solid desiccant or, if desired, dryer 43 is a glycoldryer. The thus dried gas passes on through a pipe 44 and is compressedby a compressor 45 to a pressure of about 2,550 p.s.i.a., the hotcompressed gases passing in indirect heat exchange (23) with the gasesfrom pipe 22. The compressed gas issues from exchanger 23 at about 90 F.and is passed through a pipe 46 and in indirect heat exchange withrefrigerant nitrogen in an exchanger 47. From this exchanger the chilledcompressed gas passes through a pipe 48 into a separator vessel 49.

In separator 49 a helium rich gas is removed through a pipe 50 and ispassed through a vessel 51 charged with adsorbent charcoal. From. thisabsorber the gaseous helium passes through a refrigeration economizer S2and thence leaves the system through a pipe 53 for disposal as desired.In the adsorber 51 other material than charcoal can be used providing itis suitable for removing final tracesof impurities from the helium.

Liquid separating in separator is passed therefrom through a pipe 54into about the mid-point vertically of a fractionator 56. Liquidseparated in separator 20 is also charged to fractionator 56 through apipe 55. The materials charged to the fractionator in pipe 55 are richin hydrogen and contain considerable nitrogen and are the chargematerials from which the argon product is recovered. The fractionator isoperated at'a pressure of about 400 p.s.i.a. with an overheadtemperature of about.

236 F. It is this fractionator 56 which is reboiled by the expandedcharge stock to the system in reboiler coil 14a, as mentionedhereinbefore. Overhead gaseous material leaves the fractionator throughan overhead pipe 57, a portion of this overhead material being expandedin an expander 58 to a temperature of about 360 F. This chilled andexpanded gas passes through a pipe 61 and enters a heat exchanger 60inindirect heat exchange with the remaining portion of overhead gaspassing through a pipe 59. This heat exchange is intended to producecondensate or at least to chill a portion of the overhead gas so that afinal refrigeration step-with refrigerant nitrogen will producecondensate for refluxing fractionator 56. Thus, chilled overhead gas ispassed from exchanger 64 to the refrigerated exchanger 64 for indirectheat exchange with refrigerant nitrogen from which condensate and gaspass on to a reflux accumulator 65. Condensate is passed fromaccumulator 65 at a temperature of about -290 F. through pipes 66 and 67as reflux to fractionator 56. Make-up nitrogen, as required forrefluxing, is introduced to the system through a pipe 68. Y

A preferred mode of operating fractionator 56 is to remove the argonproduct as a sidestream through a pipe 69 at a level somewhat above thatof the reboiling section of the column. The argon as removed is, ofcourse, very cold and it is passed through a refrigeration economizer 70and thence through pipe 69 for such disposal as desired. The bottomsproduct from fractionator 56, containing some argon and traces ofnitrogen, methane and ammonia, is passed through a pipe 71 for suchdisposal as desired. If desired, this bottoms product can be treated forammonia and methane removal and the remaining argon and nitrogenrecycled to pipe 11 for increasing ultimate recovery of argon; or streamfrom pipe 71 is added to the feed in pipe 11 without first removingammonia and methane because these gases are condensed in heat exchanger16 and are removed as condensate in pipe 17.

The expanded portion of the overhead gas issuing from exchanger 60 isWithdrawn from the system at a temperature of about 250 F. through apipe 62 for such disposal as desired. This material is a hydrogen andnitrogen containing product.

When a metallic oxide containing vessel, as 32 or 36, is depleted as faras the oxide content is concerned, it is regenerated by reoxidizing themetal to oxide. In FIGURE 2 vessel 36 is a second oxide containingvessel which is illustrated as being on the regeneration portion of thecycle. To regenerate the reduced metal to oxide, it is merely necessaryto pass heated air through the vessel. Thus, air from pipe 33 is pumpedby pump 34 with heat being supplied by heater 3]. and the heated air atabout 575 F. passing to vessel 36. By-pass pipe 35 by-passes a portionof the air around heater 31 in case temperature adjustment of theregeneration air is required. Off gases from the regeneration vessel 36pass therefrom through a pipe 37 to such disposal as desired.

Vessels 32 and 36 are, of course, on stream and on regenerationautomatically and the piping illustrating such automatic operation isnot shown in the drawing, for purposes of simplicity. Such piping iswell understood by those skilled in the art.

If desired, a portion of the hydrogen and nitrogen product from pipe 62is passed through a by-pass pipe 63 and through heat exchanger 12 andpassed by way of pipe 35 to the metal oxide containing vessel 36 forremoving atmospheric oxygen at the end of the regeneration portion ofthe cycle. In other words this hydrogen and nitrogen containing gaspurges excess oxygen from vessel 36 following regeneration and prior toplacing vessel 36 on steam.

As an example of the operation of the embodiment of my inventionaccording to FIGURE 2, the following tabulation illustrates compositionsof feed material, intermediate products and final products:

separating conditions and withdrawing a stream of argon therefrom asanother product of the operation.

2. A method for recovering helium and argon as sepa EXAMPLE II Materialbalance, mois per hour, principal components The values given in bothtabulations of this disclosure are in terms of mols of gas.

It will be realized by those skilled in the art that many valves,pressure and temperature indicating and/or recording devices, flowindicating and/ or recording devices and other auxiliary apparatusordinarily used in such operations are not illustrated in the drawingnor described, for purposes of simplicity. The need for such equipment,its installation and operation, are Well understood by those skilled inthe art. It is further realized that pipe and tanks and other vessels inwhich refrigerated products are passed require suitable insulation.

The flash separation in vessel 20 can, as stated relative to FIGURE 1,be carried out at a pressure higher than the 600 p.s.i.a. mentionedrelative to vessel 20. In this case more of the hydrogen is forced intothe condensate in vessel 20, and, accordingly, more hydrogen isrecovered in the product stream issuing through pipe 62.

Also, oxidation of the hydrogen in vessels 32 and 36 can be carried outprior to separation in vessel 20 but, in such cases, recovery ofhydrogen in stream 62 will be substantially eliminated. In this lattercase, after removal of the hydrogen by the metal oxide, considerablylower pressure is required for the operation of separator vessel 20 fora given helium-nitrogen separation.

It is also realized that pressures and temperatures other than thosegiven as illustrative of the operations can be used. When using otheroperating conditions, intermediate stream compositions, and productcompositions, etc. will of course, vary depending upon the particularconditions used. The herein given operating conditions are merely givenas examples of the general operation of the process.

While certain embodiments of the invention have been described forillustrative purposes, the invention obviously is not limited thereto.

1 claim:

1. A method for recovering helium and argon as separate products from agas comprising helium, argon, nitrogen and hydrogen comprising the stepsof cooling said gas to a subatmospheric temperature at asuperat-mospheric pressure thereby condensing liquid, separatingcondensed liquid from uncondensed gas as separate phases, the gas phasecomprising helium and hydrogen, and the liquid phase comprising argon,nitrogen and hydrogen, fractionating nitrogen and hydrogen from saidcondensed liquid as one product of the process, combining the remainderof the condensed liquid as bottoms from the fractionating operation withthe separated gas phase, passing this combined material into anoxidation zone and therein combining the hydrogen and any otheroxidizable gas of the combined material with atmospheric oxygen bycombustion to produce water, removing combustion effluent from saidzone, separating the so-produced Water from the effluent of theoxidation zone, chilling the water-free effiuent and condensing aportion thereof, separating uncondensed gas from condensate of thislatter operation, withdrawing this separated gas as the helium productof the operation, fractionating this latter condensate under argon rateproducts from a feed gas comprising helium, argon,- nitrogen andhydrogen under asuperatmospheric pressure comprising expanding said feedgas from said super-atmospheric pressure to a lower pressure withproduction of work whereby said gas becomes cooled, chilling the cooledgas and separating a liquid phase from a gas phase, the liquid phasecomprising argon, nitrogen and hydrogen and said gas phase comprisinghelium and nitrogen, fraction-- ating said liquid phase therebyproducing an overhead gasproduct and a bottoms liquid, compressing airby thework produced in the aforementioned expanding of said feed gas,cooling this compressed air by indirect heat ex-- change with a coolingagent and introducing this com-- pressed and cooled air into theaforementioned fractionating operation and fractionating this cooled airand said liquid phase, said overhead product comprising hydrogen: andnitrogen and said bottoms liquid comprising argon: and oxygen, combiningthis bottoms liquid with the afore-- mentioned gas phase, passing thiscombined material into a combution zone and therein reacting bycombustion theoxygen and hydrogen to form water, removing effluent fromthe combustion zone and dehydrating the. eflluent, compressing andchilling the dehydrated efiluent thereby producing condensate,separating uncondensed gas from: this latter condensate, the separatedgas being the helium: product of the operation, fractionating saidlatter con-- densate and thereby producing argon as another product ofthe operation.

3. The operation of claim 2 wherein said feed gas comprises helium,argon, nitrogen, hydrogen, methane, and ammonia, the first-mentionedliquid phase comprises: argon, nitrogen, hydrogen, methane and ammonia,the: aforementioned bottoms liquid comprises argon, oxygen, methane andammonia, and in said combustion zone re-- acting said oxygen withhydrogen and said methane and ammonia, removing carbon dioxide from thecombustion zone effluent prior to said dehydration step, and passing antoverhead gas from the final argon fractionation step into thefirst-mentioned fractionating step.

4. The operation of claim 2 wherein the chilling steps are carried outby indirect heat exchange with refrigerant liquid nitrogen.

5. In the operation according to claim 2, producing reflux for thefirst-mentioned fractionation step by dividing the overhead gas productof this fractionation step into two portions, expanding one portion to alower pressure with the production of work whereby said one portion iscooled, cooling the other portion by indirect heat exchange with theexpanded and cooled portion, chilling the cooled other portion to astill lower temperature by indirect heat exchange with refrigerantliquid nitrogen whereby condensate is formed, and passing this so-formedcondensate into said first-mentioned fractionation step as. said reflux.

6. A method for recovering helium from a feed gas which is a syntheticammonia plant ofi-gas comprising helium, argon, nitrogen and hydrogen,comprising the steps of cooling said gas to a subatmospheric temperatureat a superatmospheric pressure of about 4,700 pounds per square inchabsolute thereby producing liquid containing a major proportion of thehydrogen of the gas and argon, separating'the uncondensed gas from saidliquid, the uncondensed gas comprising helium and a minor proportion ofthe hydrogen of the feed gas, expanding said unco-ndensed gas from saidsuperatmospheric to a lower superatmospheric pressure with theproduction of work, compressing air by the work produced in the gasexpanding operation, expanding in a second expanding operation saidliquid from said superatmospheric pressure whereby at least a portionthereof is vaporized with the production of Work, further compressingthe previously compressed air by the work produced in the secondexpanding operation, chilling the further compressed air, fractionatingthe vapors and the unvaporized liquid of the second expanding operationand the chilled further compressed air with the production of anoverhead gas product comprising hydrogen and a liquid product comprisingargon and oxygen, passing this liquid product and the uncondensed gascomprising helium and hydrogen into a com- References Cited in the fileof this patent UNITED STATES PATENTS 1,658,631 Dannenbaum Feb. 7, 1928-2,019,632 Ray Nov. 5, 1935 2,530,602 Dennis Nov. 21, 1950 2,545,778Haringhuizen Mar. 20, 1951 2,713,781 Williams July 26, 1955 2,826,480Webster Mar. 11, 19'58 OTHER REFERENCES Gas Liquefaction and LowTemperature Rectification, Davies, published by Longmans, Green andCompany, In-

20 corporated, New York, pages 178 and 179.

